# Lane Following Autopilot with Keras & Tensorflow.

Posted on January 12, 2017 in notebooks,

This document walks through how to create a convolution neural network using Keras+Tensorflow and train it to keep a car between two white lines.

Updated Feb 2, 2017 - Thanks to comments on Hacker News, I've updated this doc to use more machine learning best pratices.

Here is a Raspberry Pi controlled RC car using the autopilot crated in this document to drive between the lines. See the donkey repository for instructions to build your own car.

In [1]:
import os
import urllib.request
import pickle

%matplotlib inline
import matplotlib
from matplotlib.pyplot import imshow


### Get the driving data¶

The dataset is composed of ~7900 images and steering angles collected as I manually drove the car. About 2/3 of the images are with the car between the lines. The other third is of the car starting off course and correcting by driving back to between the lines.

In [2]:
#downlaod driving data (450Mb)
data_url = 'https://s3.amazonaws.com/donkey_resources/indoor_lanes.pkl'
print(file_path)

/tmp/tmpjjuhirpf


The dataset consists of 2 pickled arrays. X are the image arrays and Y is an array of the coresponding steering angles.

In [3]:
#extract data
with open(file_path, 'rb') as f:

print('X.shape: ', X.shape)
print('Y.shape: ', Y.shape)
imshow(X[0])

X.shape:  (7892, 120, 160, 3)
Y.shape:  (7892,)

Out[3]:

### Split Data¶

Here we'll shuffle our data and separate the data into three parts. Training data will be used to train our driving model, Validation data is used avoid overfitting the model and Test data is used to test if our model learned anything.

In [4]:
import numpy as np

In [5]:
#shuffle  both X and Y the same way
def unison_shuffled_copies(X, Y):
assert len(X) == len(Y)
p = np.random.permutation(len(X))
return X[p], Y[p]

shuffled_X, shuffled_Y = unison_shuffled_copies(X,Y)

len(shuffled_X)

Out[5]:
7892
In [6]:
test_cutoff = int(len(X) * .8) # 80% of data used for training
val_cutoff = test_cutoff + int(len(X) * .1) # 10% of data used for validation and test data

train_X, train_Y = shuffled_X[:test_cutoff], shuffled_Y[:test_cutoff]
val_X, val_Y = shuffled_X[test_cutoff:val_cutoff], shuffled_Y[test_cutoff:val_cutoff]
test_X, test_Y = shuffled_X[val_cutoff:], shuffled_Y[val_cutoff:]

len(train_X) + len(val_X) + len(test_X)

Out[6]:
7892

### Augment Training Data¶

To double our training data and prevent steering bias, we flip each image and steering angle and add it to the dataset. There are additional ways to augment driving data using translations and fake shadows but I didn't use those for this autopilot.

In [7]:
X_flipped = np.array([np.fliplr(i) for i in train_X])
Y_flipped = np.array([-i for i in train_Y])
train_X = np.concatenate([train_X, X_flipped])
train_Y = np.concatenate([train_Y, Y_flipped])
len(train_X)

Out[7]:
12626

### Build a driving model¶

This driving model will be an end-to-end neural network that accepts image arrays as input and outputs a steering angle between -90 (left) and 90 (right). To do this we'll use a 3 layer convolution network with one fully connected layer. This model is based off of Otavio's Carputer but does not produce a throttle value output, does not use past steering values as input into the model, and uses one less convolution layer.

In [8]:
from keras.models import Model, load_model
from keras.layers import Input, Convolution2D, MaxPooling2D, Activation, Dropout, Flatten, Dense

Using TensorFlow backend.

In [9]:
img_in = Input(shape=(120, 160, 3), name='img_in')
angle_in = Input(shape=(1,), name='angle_in')

x = Convolution2D(8, 3, 3)(img_in)
x = Activation('relu')(x)
x = MaxPooling2D(pool_size=(2, 2))(x)

x = Convolution2D(16, 3, 3)(x)
x = Activation('relu')(x)
x = MaxPooling2D(pool_size=(2, 2))(x)

x = Convolution2D(32, 3, 3)(x)
x = Activation('relu')(x)
x = MaxPooling2D(pool_size=(2, 2))(x)

merged = Flatten()(x)

x = Dense(256)(merged)
x = Activation('linear')(x)
x = Dropout(.2)(x)

angle_out = Dense(1, name='angle_out')(x)

model = Model(input=[img_in], output=[angle_out])
model.summary()

____________________________________________________________________________________________________
Layer (type)                     Output Shape          Param #     Connected to
====================================================================================================
img_in (InputLayer)              (None, 120, 160, 3)   0
____________________________________________________________________________________________________
convolution2d_1 (Convolution2D)  (None, 118, 158, 8)   224         img_in[0][0]
____________________________________________________________________________________________________
activation_1 (Activation)        (None, 118, 158, 8)   0           convolution2d_1[0][0]
____________________________________________________________________________________________________
maxpooling2d_1 (MaxPooling2D)    (None, 59, 79, 8)     0           activation_1[0][0]
____________________________________________________________________________________________________
convolution2d_2 (Convolution2D)  (None, 57, 77, 16)    1168        maxpooling2d_1[0][0]
____________________________________________________________________________________________________
activation_2 (Activation)        (None, 57, 77, 16)    0           convolution2d_2[0][0]
____________________________________________________________________________________________________
maxpooling2d_2 (MaxPooling2D)    (None, 28, 38, 16)    0           activation_2[0][0]
____________________________________________________________________________________________________
convolution2d_3 (Convolution2D)  (None, 26, 36, 32)    4640        maxpooling2d_2[0][0]
____________________________________________________________________________________________________
activation_3 (Activation)        (None, 26, 36, 32)    0           convolution2d_3[0][0]
____________________________________________________________________________________________________
maxpooling2d_3 (MaxPooling2D)    (None, 13, 18, 32)    0           activation_3[0][0]
____________________________________________________________________________________________________
flatten_1 (Flatten)              (None, 7488)          0           maxpooling2d_3[0][0]
____________________________________________________________________________________________________
dense_1 (Dense)                  (None, 256)           1917184     flatten_1[0][0]
____________________________________________________________________________________________________
activation_4 (Activation)        (None, 256)           0           dense_1[0][0]
____________________________________________________________________________________________________
dropout_1 (Dropout)              (None, 256)           0           activation_4[0][0]
____________________________________________________________________________________________________
angle_out (Dense)                (None, 1)             257         dropout_1[0][0]
====================================================================================================
Total params: 1,923,473
Trainable params: 1,923,473
Non-trainable params: 0
____________________________________________________________________________________________________


### Train the model.¶

I've learned the hard way that even if everything to this point is perfect, your autopilot won't work if you don't train it correctly. The biggest problem I ran into was over fitting the model so that it would not work in evenlly slightly different scenarios. Here are 2 Keras callbacks that will save you time.

Warning - This will take a long time (3hrs) if only using a CPU

I ran this notebook on my Dell XPS notebook that does not have a CUDA compatible GPU so it's very slow and freezes. To speed up training you can uses a EC2 instance with a GPU. Several instance images exist with Keras and Tensorflow already loaded.

In [10]:
import os
from keras import callbacks

model_path = os.path.expanduser('~/best_autopilot.hdf5')

#Save the model after each epoch if the validation loss improved.
save_best = callbacks.ModelCheckpoint(model_path, monitor='val_loss', verbose=1,
save_best_only=True, mode='min')

#stop training if the validation loss doesn't improve for 5 consecutive epochs.
early_stop = callbacks.EarlyStopping(monitor='val_loss', min_delta=0, patience=5,
verbose=0, mode='auto')

callbacks_list = [save_best, early_stop]


For this notebook, I'll only train the model for 4 epochs.

In [11]:
model.fit(train_X, train_Y, batch_size=64, nb_epoch=4, validation_data=(val_X, val_Y), callbacks=callbacks_list)

Train on 12626 samples, validate on 789 samples
Epoch 1/4
12608/12626 [============================>.] - ETA: 0s - loss: 821.4849   Epoch 00000: val_loss improved from inf to 516.59291, saving model to /home/wroscoe/best_autopilot.hdf5
12626/12626 [==============================] - 384s - loss: 822.5694 - val_loss: 516.5929
Epoch 2/4
12608/12626 [============================>.] - ETA: 0s - loss: 430.3060  Epoch 00001: val_loss improved from 516.59291 to 384.87241, saving model to /home/wroscoe/best_autopilot.hdf5
12626/12626 [==============================] - 400s - loss: 430.4499 - val_loss: 384.8724
Epoch 3/4
12608/12626 [============================>.] - ETA: 0s - loss: 348.3565  Epoch 00002: val_loss improved from 384.87241 to 321.23424, saving model to /home/wroscoe/best_autopilot.hdf5
12626/12626 [==============================] - 328s - loss: 348.1003 - val_loss: 321.2342
Epoch 4/4
12608/12626 [============================>.] - ETA: 0s - loss: 304.5375  Epoch 00003: val_loss did not improve
12626/12626 [==============================] - 327s - loss: 304.4417 - val_loss: 326.8560

Out[11]:

### Evaluate Performance¶

We can check if our models predictions are reasonable by plotting the predictions vs the actual values. The first graph shows that there is a learned relationship in our test data (not seen by model during training).

In [12]:
import pandas as pd

test_P = model.predict(test_X)
test_P = test_P.reshape((test_P.shape[0],))

In [13]:
df = pd.DataFrame({'predicted':test_P, 'actual':test_Y})
ax = df.plot.scatter('predicted', 'actual')
#ax.set_ylabel("steering angle")


This second graph uses the unshuffled data that includes the training data to show the predicted angles closely follow the actual steering angles.

In [14]:
P = model.predict(X[:700])
#predict outputs nested arrays so we need to reshape to plot.
P = P.reshape((P.shape[0],))

ax = pd.DataFrame({'predicted':P, 'actual':Y[:700]}).plot()
ax.set_ylabel("steering angle")

Out[14]:

## Next steps¶

• Improve Model This model is naive because it doesn't use past values to help predict the future. We could experiment with the model by feeding past steering angles as inputs to the model, add a recurrent layer, or just change the structure of the convolution layers.
• Add more data This model will improve as we add more driving data.
• Predict throttle outputs Currently the autopilot only steers and maintains a constant speed. A more sophisticated model would speed up on straightaways and slow down before curbs.
In [ ]: